Corrosive chemicals are kept in large vessels for various reasons, such as storage or for carrying out chemical or physical reactions involving such corrosive chemicals. For large industrial applications, metallic vessels are usually preferred, because of the high strength per given weight and cost of metals as a structural material. Unfortunately, many metals are corroded by many chemicals, requiring a vessel lining to protect the metal vessel from such corrosion. As used herein, the term "vessel" refers to the metallic portion only, i.e., the structural member for containment of the corrosive chemical. The term "container" refers to the vessel and the vessel lining which protects the vessel.
Various polymeric materials, frequently containing fluorine or other halogen, and in particular, polyvinylidene fluoride, have been suggested for use in vessel linings. Vinylidene fluoride polymers are well-known resins, extremely useful in protective coatings for a variety of substrates, including metal, because of the excellent chemical resistance, thermal stability, etc., of the resin. Polymerization techniques used in preparation of vinylidene fluoride polymers are described, for example, in Hauptschein, U.S. Pat. No. 3,193,539. Coatings consisting only of polymers, however, are subject to delamination, cracking, shrinking, blistering, swelling, floating, scaling, and peeling. Accordingly, various proposals have been made in the prior art to supplement the polyvinylidene fluoride or other polymeric material in order to prevent such failure of the coating.
For example, Dukert, et al., U.S. Pat. No. 3,779,854, suggests the use of a polyvinylidene fluoride laminate construction containing, for example, glass cloth, yarn or roving, in order to provide a coating having greater strength and greater impermeability.
Segawa, et al., U.S. Pat. No. 3,824,115, suggests the use of polyvinylidene fluoride compositions containing an inorganic substance having a size of 50-325 mesh (44-297 microns), of a material such as silica, graphite, molybdenum disulfide or chromium oxide, in the undercoat (only) coating to be applied to a metal substrate to be subjected to corrosive chemical. Over the undercoating containing the inorganic substance, Segawa et al require the application of an overcoat, having a thickness of from 1/4 to 4 times that of the undercoat, the overcoat containing no such inorganic filler (although depending on the necessity, other substances such as pigments, fillers, and nucleating agents may be added to the Segawa, et al. overcoat). The intent of Segawa, et al., as that of Dukert et al, appears to be the presentation of an impermeable coating, continuous and without gaps or pinholes.
The polyvinylidene fluoride coatings of Dukert et al and Segawa et al, although having certain ability to resist corrosive chemical, are nonetheless subject to delamination, blistering, or other failure, under sufficiently severe conditions. Accordingly, it is an object of the present invention to provide a corrosive chemical containment system with greater resistance to delamination, blistering, and other failure.